To acquire an X-ray projection image, the tube, patient and detector have to be positioned relative to each other. For example, this is performed by a technician as a manual task. An X-ray source may be provided with a light visor such that the technician can see where the actual X-ray beam would be positioned. The light visor projects light from the tube to indicate, for example, centre and collimation of the X-ray beam that will result from the current positioning. Thus, the technician moves the X-ray source, as well as the patient, until a desired spatial relation has been achieved. For example, WO 2004/034909 A1 describes a light pointer for a radiographic device. However, the procedure of positioning may be time-consuming due to the necessary movement of the X-ray source itself.